SAN FRANCISCO — Three man have been charged with either selling methamphetamine or guns to undercover federal agents, including one Oakland man who allegedly used his houseboat on the Oakland marina to peddle firearms and brag about his knack for making customized bullets. In two federal cases, prosecutors have charged Aleksandr Akopov, Jacob Horowitz, and Vadim Kazakevich with federal offenses related to an undercover ATF and DEA investigation based in Oakland and San Francisco. Prosecutors allege he did this through his connections to both Horowitz — an alleged methamphetamine dealer who lived in San Francisco — and Kazakevich, an alleged gun trafficker with a houseboat at the Oakland marina. On Sept. 15, DEA agents raided Horowitz’s home on the 100 block of Farragut Avenue in San Francisco and seized nine pounds of methamphetamine, according to the criminal complaint against him. During one meeting, Kazakevich reportedly bragged about his ability to make or acquire bullets for nearly every occasion.